1. Field of the Invention
The present invention relates to a contact mechanism in an electromagnetic switchgear having a coil lead portion to be connected to an external terminal.
2. Prior Art
FIG. 4 is an overall sectional view of a conventional electromagnetic switchgear.
An electromagnetic switchgear 1 of the sort shown in FIG. 4 has a magnetic path casing 2, and an exciting coil 3 which is wound on a plastic bobbin 4. The exciting coil 3 consists of an absorbing coil 3a of thick conductor and a holding coil 3b of thin conductor. A spool 31 for winding the coils is provided at the rear end of the bobbin 4; the lead conductor 30a of the absorbing coil 3a and the lead conductor 30b of the holding coil 3b are led out therefrom, respectively. Further, the electromagnetic switchgear 1 further has a fixed iron core 5, a guide bushing 6 made of non-magnetic material, the guide bushing 6 being fitted to the inner periphery of the bobbin 4 and secured to the fixed iron core 5, a moving iron core 7 opposite to the fixed iron core 5, the moving iron core 7 being supported in such a way that it is slidable on the inner periphery of the guide bushing 6 in the axial direction, a hook 8 with its rear end portion inserted into a hole 7a bored in the moving iron core 7, and a shift lever 9 for moving a start overrunning clutch (not shown), the upper end of the shift lever 9 being coupled to the hook 8. Further, the electromagnetic switchgear 1 has a spring receptacle 10 secured at the outlet of the hole 7a, a buffer spring 11 for pressing the hook 8 in the backward direction, a reset spring 12 for advancing and resetting the moving iron core 7, and a resin-molded cap 13 coupled via a rubber packing 14 to the end of the fixed iron core 5 and caulked at the end of the magnetic path casing 2. Moreover, the electromagnetic switchgear 1 has a pair of fixed contacts 15a, 15b (only one of which is shown), their terminal bolts 16 being passed through the cap 13 outwardly and fixed. The terminal of a lead wire from a power supply (storage battery) is connected to one terminal bolt 16, whereas the terminal of a lead wire for the brush of an electric motor is connected to the other terminal bolt. In addition, the electromagnetic switchgear 1 has a moving contact 20 opposite to the pair of fixed contacts 15a, 15b and supported with a moving rod 21 via an insulating member 22, a retaining ring 23, a compression spring 24 for giving the moving contact 20 a contact pressure, a compression spring 25 for advancing and resetting the moving rod 21, and an external terminal 32 connected to the lead conductors 30a, 30b of the coils with solder 33, the external terminal 32 also being connected to a lead wire from a start switch of an internal combustion engine.
The operation of the electromagnetic switchgear will subsequently be described. When the start switch (not shown) is actuated, the absorbing coil 3a and the holding coil 3b are caused to conduct and the moving iron core 7 is attracted to the fixed iron core 5 and thereby moves back. The hook 8 also moves back to rotate the shift lever 9, thus advancing the overrunning clutch (not shown). On the other hand, the moving contact 20 that is geared to the backward movement of the moving iron core 7 is moved back to close the fixed contacts 15a, 15b. Power is thus supplied to the circuit of the electric motor so as to rotate its armature.
A description will then be given of the state in which the external terminal 32 is kept in contact with the lead conductors 30a, 30b with reference to FIGS. 5, 6. As shown in FIGS. 5, 6, the external terminal 32 is mounted on the cap 13 with an eyelet 34, whereas the lead conductors 30a, 30b of the coils are led out of an outlet hole 34a of the eyelet 34 and secured thereto with solder 33. The lead conductors 30a, 30b are thus electrically connected to the external terminal 32.
In the prior art example of FIG. 5, the known practice is to insert an insulating tube 35 into the eyelet 34 to prevent the solder 33 from sagging into the electromagnetic switchgear from the gap between the inner periphery of the eyelet 34 and the lead conductors 30a, 30b of the coils.
FIG. 6 illustrates an eyelet 34 whose inner diameter has been reduced to decrease the gap between the inner periphery of the eyelet 34 and the lead conductors 30a, 30b.
In the case of the conventional electromagnetic switchgear, it is advantageous to use such a common eyelet 34 for securing the external terminal 32 when not only the number of parts but also processability is taken into consideration. This naturally tends to render the inner diameter of the eyelet 34 greater. Consequently as shown in FIG. 5, the insulating tube 35 is required to prevent solder from sagging during the process of soldering the lead conductors 30a, 30b of the coils. Notwithstanding, the laborious work of inserting the insulating tube 35 still makes it difficult to mechanize this process and besides complete solder-sagging prevention remains unaccomplished.
Even into the reduced inner diameter as shown in FIG. 6, the eyelet 34 still fails to ensure complete solder-sagging prevention, and for this reason, makes it difficult to insert the lead conductors 30a, 30b of the coils into the inner periphery of the eyelet 34, thus causing the faulty insertion of lead conductors.